Knowing your lines.
That intro picture is pretty typical of a lot of chess tutorial. That's why we call them "lines". They have names, usually who ever invented the opening but sometimes it's a place name, but no matter what, you have to learn them. At least a good repertoire of Black and White.
For beginners I don't recommend "theory heavy" lines like the Caro-Kann. Its defense for Black and oh my God the book I've got on it. I bought the book probably two years ago and I'm still only half way through it. I've got a couple of regulars from my friends list who will tell me, "you have to play White, so you can't use the Caro-Kann".
Easier stuff like Van't Kruiz, Scandanavian or Italian games are much better suited to lower level and relative beginner players. You can't just go do as you please in this game because someone who knows even a few lines will kick your ass around the board.
I like to bring up GothamChess and Levy Rozman because he loves to make fun of his students or opponents who just do stupid stuff. I'm not even going to link to any of those vids because they're not hard to find on his video blog. Just look for the words "I Quit!".
He's never really quits but it's sure fun to watch him pull his hair out. In other news about Levy Rozman, he was just recently awarded Chess Master and published a book that is well worth reading (How to win at Chess; ISBN Hard Cover, 978024167673e: ebook 9781802064506).
Pushing Pawns forward into a Sawtooth is technically a "line", but there are so many that are so much better. If you need a reference I recommend Anna Cramling who has a great series on "If you're under ...." you should watch this video. She breaks it down to 400, 800, 1000, 1200 and I think she's working on a 1600 level video too.
If you are starting to wonder why you regularly lose to particular regular opponents. They've got your number and know what you're going to. You might do against others who don't know your regular silly mistakes, but the nice ones among with show you.
What silly mistakes do you make? Me? I regularly miss one move checkmates and I don't know why.